Radio wave propagation through vegetation: Factors influencing signal attenuation

Abstract

[1] The paper describes an extensive wideband channel sounding measurement campaign to investigate signal propagation through vegetation. The measurements have been conducted at three frequencies (1.3, 2 and 11.6 GHz) at sites with different measurement geometries and tree species. The data have been used to evaluate current narrowband empirical vegetation attenuation models and study the prevailing propagation mechanisms. Evaluation of the modified exponential decay (MED), maximum attenuation (MA) and nonzero gradient (NZG) models show that on a site by site basis, the NZG model gives the best prediction of excess attenuation due to vegetation. The MA model has been found to be the worst of the three models. The studies have shown that the measurement site used to obtain the NZG model parameter values given in International Telecommunication Union (ITU) [2001] is influenced by metal lampposts and passing traffic, and thus was based on corrupted data. The results show that the leaf state, measurement geometry and vegetation density are more important factors influencing signal attenuation than tree species or leaf shape. Generally, the 11.6 GHz signal was attenuated much more than the 1.3 and 2 GHz signals by vegetation in-leaf, but the differences in attenuation were not significant in the out-of-leaf state. A successful excess attenuation model due to vegetation must consider the measurement geometry and vegetation descriptive parameters as well as any contributions from ground reflection and/ or diffraction over the top or round edges of the trees.

Development of the measurement method for challenging NLOS conditions in mobile networks

“…This effect is expected as many studies have reported the decrease of the attenuation of trees without foliage e.g. [6], [7] and [8]…”

“…There are many studies e.g., [6], [7] and [8], which have reported the seasonal effect i.e., the increase in the attenuation of trees inleaf compared with the out-of-leaf state.…”

Investigations of Foliage Effect on Modern Wireless Communication Systems: A Review

“…Different parameter values have been proposed depending on the frequency, foliage type, and propagation mechanisms etc. The advantage of the exponential decay model lies in its simplicity, but it has a major drawback that it does not take into account the measurement geometry as indicated by Savage et al in [19].…”

“…From these comparative works [13,[17][18][19], it can be found that taking into the consideration of the measurement geometry, tree species, leaf shape and foliated state, the NZG model is the better method of the foliage loss prediction at the microwave and millimeter wave as compared to other models in Table 1. However, as pointed out by Savage et al [19], the values obtained at one site for the NZG model may not be used to predict attenuation at another because they encompass propagation anomalies that may not exist at both sites.…”

“…From his results, the NZG model is shown to be a better model for the foliage loss prediction considering both the tree species and foliated state. Recently, Savage et al [19] have conducted impressive comparative studies among the MED model, MA model and NZG model at 1.2 GHz, 3 GHz, and 11.6 GHz. It is noted that they used the original exponential decay model as shown in Equation (1) to fit the measured data for the study of the MED model.…”